1. Field of the Invention
The present invention relates to a plasma processing method and apparatus, and more particularly to the plasma processing method and apparatus which are suited to treat the surface of an element like a semiconductor element through the effect of the plasma.
2. Description of the Related Art
As a technology of processing the surface of a substrate of a semiconductor element of the line through the effect of the plasma, as disclosed in Samakawa U.S. Pat. No. 5,827,435, there has been known a plasma processing method which is arranged to take the steps of generating positive ions in sufficient density by discharging the ECR plasma for about 10 xcexcsec, stopping the discharge for 100 xcexcsec for generating a massive number of positive and negative ions, at the same time, applying a RF electric field of 600 kHz into the ions only when the discharge is turned off, and charging only the positive and negative ions having the same mobility onto the substrate for suppressing charging caused by the difference of the mobility among the electrons and ions.
Further, Otsubo et al U.S. Pat. No. 4,808,258 discloses the plasma processing apparatus which is arranged to control distribution of the electron temperature of the plasma and an occurrence ratio of reactive materials such as ions and radicals generated in the plasma according to the reactive conditions by periodically modulating a microwave power and at once controlling the energy distribution of ions charged into a material to be processed from the plasma according to the reaction by periodically changing the voltage to be applied for accelerating the ions to be charged into the material to be processed from the plasma.
Moreover, Ooiwa et al U.S. Pat. No. 4,891,118 and the Doki et al U.S. Pat. No. 5,160,397 disclose the plasma processing apparatus which is arranged to synchronize the occurrence time of a pulse-wise microwave with that of a RF bias voltage.
With recent enhancement of integrity of a semiconductor integrated circuit, for example, it is likelihood that the gate oxide file of a MOS (Metal Oxide Semiconductor) transistor that is one representative semiconductor is made thinner and the working aspect ratio of the device structure is made larger by making the minimal working dimensions minute. In this kind of microstructure element, the electrons having large random kinetic components caused by the mass difference among the electrons and the ions are captured by the pattern and thereby cannot reach the groove bottom. It means that the groove bottom is shorter of electrons rather than the ions reached on the groove bottom and is thereby charged positively. This phenomenon is called electron shading. This phenomenon brings about a shortcoming that a potential difference is caused between an open area and a line and space area and thereby the gate oxide file is charging-damaged.
The technology disclosed in the foregoing U.S. Pat. No. 5,827,435 is arranged to apply a RF electric field of 600 kHz when the discharge is turned off, charge only the positive and negative ions having the same mobility onto the substrate, and thereby suppress the charging. However, the experiment performed by the inventors of the present application indicated that the charging damage may have an adverse effect on the amounts of electrons and ions flown into the sparse portion with no pattern. The present prior art does not mention the method of suppressing the charging damage, which method is mentioned by the present invention.
Moreover, U.S. Pat. Nos. 4,808,258, 4,891,118, and 5,160,397 do not mention the method of suppressing the charging damage, which method is mentioned by the present invention.
It is an object of the present invention to provide a plasma processing method and apparatus which are configured to suppress the charging damage due to a device structure, thereby making it possible to process the surface with high precision.
In carrying out the object, according to an aspect of the invention, a plasma processing method for processing an object to be processed such as a substrate using a plasma comprises controlling generation of the plasma and incident energy of ions in the plasma to the object independently of each other, wherein, the plasma is intermittently generated and as short as 10 xcexcsec are secured as an off time of the plasma generation after the plasma discharge is turned off.
According to another aspect of the invention, a plasma processing method for processing a substrate using a plasma comprises controlling generation of the plasma and incident energy of ions in the plasma to the substrate independently of each other wherein, the plasma is intermittently generated and an off time of the plasma generation after the plasma discharge is turned off is secured such that the ratio of negative current to positive current flowing into the substrate is made 10 or less.
According to another aspect of the invention, a plasma processing method for processing a substrate using a plasma comprises controlling generation of the plasma and incident energy of ions in the plasma to the substrate independently of each other wherein, the plasma is intermittently generated at a period of 1 kHz to 90 kHz, the duty ratio is adjusted as 10% or more, and the off time of the plasma generation after the plasma discharge is turned off is secured to have 10 xcexcsec.
According to another aspect of the invention, in a plasma processing method performed by a plasma processing apparatus including a decompression processing chamber connected to a vacuum exhaust device, a gas supply device for supplying gas to the processing chamber, a plasma generating source having a high frequency power supply for generating time-modulated plasma in the processing chamber, a substrate electrode on which a material to be processed is to be placed, and a bias power supply for supplying a high frequency bias power to the substrate electrode, the high frequency power provided by the plasma generating source is time-modulated such that the occupation ratio of the period of modulating the time of the plasma to the time when the ratio of the negative current to positive current flowing into the substrate is 10 or less to is 40% or more.
In carrying out the object, in a plasma processing apparatus having a decompression processing chamber connected to a vacuum exhaust device, a gas supply device for supplying gas to the processing chamber, a plasma generating source having a high frequency power supply for generating the time-modulated plasma in the processing chamber, a substrate electrode on which a material to be processed may be placed, and a bias power supply for supplying a high frequency bias electric power to the substrate electrode, the high frequency electric power for generating the plasma provided in the plasma generating source is time-modulated so that 40% or more is an occupation ratio of the period of time-modulating the plasma to the time when the ratio of the negative current to positive current flowing into the substrate is 10 or less.
Further, the repetitive frequency of the high frequency power supply for generating the plasma ranges from 1 kHz to 90 kHz and the pulse duty ratio thereof is 60% or less.
Moreover, the high frequency bias electric power to be supplied onto the substrate is time-modulated at a repetitive frequency of 1 kHz or more and a duty ratio of 60% or less.
According to another aspect of the invention, in a plasma processing apparatus having a decompression processing chamber connected to a vacuum exhaust device, a gas supply device for supplying gas to the processing chamber, a plasma generating source having a high frequency power supply for generating the time-modulated plasma in the processing chamber, a substrate electrode on which a material to be processed may be placed, and a bias power supply for supplying a high frequency bias electric power to the substrate electrode, the high frequency electric power for generating the plasma is time-modulated such that 20% or less is an occupation ratio of the period of time-modulating the plasma to a time when negative and positive currents flowing into the substrate are equal to each other.
Further, the repetitive frequency of the high frequency power supply for generating the plasma ranges from 1 kHz to 90 kHz and the pulse duty ratio thereof is 60% or less.
Moreover, the high frequency bias electric power is time-modulated at a repetitive frequency of 1 kHz or more and a duty ratio of 60% or less.
According to another aspect of the invention, in a plasma processing method for processing the substrate as controlling generation of the plasma and incident energy of ions in the plasma to the substrate independently, the plasma is intermittently generated at a period of 1 kHz to 90 kHz, the duty ratio is 10% or more, and the time after the plasma discharge is turned off is secured to have 10 xcexcsec, and the bias voltage for controlling the incident energy of ions is time-modulated.
Further, the time modulation of the bias voltage is synchronized with the period of generating the plasma.
According to an aspect of the invention, the method comprises the steps of carrying out the pulsed discharge by switching on and off the high frequency electric power for generating the plasma, controlling the off time of the pulsed discharge when the ratio of electron saturated current to ion saturated current (often referred to as the electron/ion saturated current ratio) is less than the predetermined value, controlling an inflow quantity of positive and negative charges to the sparse portion and the dense portion of the device patterns, and thereby suppressing the charging damage.
According to another aspect of the invention, the plasma processing apparatus is arranged to control an off time by switching on and off the high frequency electric power for generating the plasma to be charged, controlling the ratio of positive charges to negative charges to be flown into the sparse portion and the dense portion of the device patterns, and suppressing the voltage generated on a gate oxide film, thereby suppressing occurrence of the charging damage. This makes it possible to perform the highly accurate etching treatment.